Labbing a P5X
 

I was finally able to make some runs this morning to test out the P5Xs on my single step 35 Fountain. These props really hook up! I was able to increase my speed from 95 to 98 mph. The 95 was attained with stock 32 Bravos, while the 98 was achieved with stock 31 P5Xs. Both turning 5600 rpm. On the dyno I should be turning 5800 for peak hp. Is it worth it to lab the P5Xs. I know the Bravo responds well to labbing, but have been told that the Hydromotives are better stock. If, so do I have the right pitched prop?

You're only 200 rpm off. I'm sure labbing will get you back your rpm, but also, it's summer. Your engine is making less hp. My 2 cents is to wait for cooler times and then run these props again. You should get back that 200 rpm. If you lab now, you might start putting it into the rev limiter in cooler weather.

True Greg. Your RPM may indeed go up in the shoulder seasons so it is important to prop to your goals. I would not be as quick to lab the P5X props they are great stock. THe only other thing that may be a consideration is trying a semi-cleaver propeller to see how she handles the addtional lift.

Julie

Great numbers, you should break 100 this fall!

Another thought here....... Often the prop wizzards will advise that you prop to your torque curve not just your peak horsepower. What I've seen / heard is to go 1200 RPM over your peak torque. Where is your peak torque number?

I would also agree that as the weather changes you will make more HP and pick up some R's. Naturally asperated motors are often more affected by bad air than a blown set up. My intercooled 525 SC's were pretty consistent, the intercoolers were the big reason. You might well end up with two sets of props, a spring / fall set and a set for the hot sticky days.

Here are my numbers from the dyno sheet starting at 5000. Any light shed from these numbers on how to prop? Thanks.

RPM TRQ HP
5000 692 659
5100 692 672
5200 690 683
5300 676 682
5400 663 682
5500 662 693
5600 654 698
5700 646 702
5800 642 709
5900 618 695
6000 607 693
6100 589 684
6200 546 645

5800 RPM which will put you 700 above peak torque.

Julie

Is that a pretty good rule of thumb, or does it vary greatly, by size/weight, and hull design?

bingo,,,,,,,,,,



also steped , notched, paded, etc,,,


i vote for 2 set's of props.

Yes it can vary. But a standard on stock motors is about 1100-1200 RPM difference between peak torque and peak HP. With modified motors this changes. Although we would like to see some distance or RPM between them. As running to close to peak torque has consequences.

Julie